Vincoleukoblastine (VLB, vinblastine) was the first of the dimeric indole alkaloids to be used in the treatment of malignancies. The compound is the subject of U.S. Pat. No. 3,097,137, to Beer, Cutts and Noble. The next of the dimeric indole alkaloids to be used in the treatment of malignancies, and in particular of the acute leukemias of childhood, was leurocristine (vincristine)--see U.S. Pat. No. 3,205,220 to Svoboda, Barnes and Armstrong. Also claimed in this latter patent was the dimeric vinca alkaloid, leurosidine, an isomer of VLB. VLB, vincristine, and leurosidine can all be represented by Formula I below as follows: ##STR1##